The present invention relates to a large-current circuit board including a plurality of fasteners for applying relatively large current to a circuit board and a plurality of busbars for connecting the plurality of fasteners. It also concerns methods of assembly therefor. 2. Description of the Background Art
FIG. 34 is a perspective view showing a printed wiring board (printed circuit board) known in the art serving as a large-current circuit board disclosed in Japanese Laid-Open Patent Publication SH062-257191. In this drawing, the numeral 801 indicates a printed wiring board, 802 denotes an insulating board, 803A, 803B, 804A and 804B represent circuit patterns, 805A and 805B designate conductor plates, 806 and 807 indicate terminal holes, and 808 denotes holes used for soldering.
In the example of FIG. 34, the electrically conductive circuit patterns 803A, 803B, 804A, 804B are formed on the insulating board 802, the electrically conductive plates 805A, 805B having a similar shape to the patterns 804A, 804B are applied and joined to at least part of the circuit patterns 803, and the circuit board is applicable to a circuit carrying current of several ten amperes or more.
While this conventional art is effective for the application of large current in the plane direction of the board, it is difficult to apply large current in the vertical direction of the board, i.e., through hole direction. Further, since the electrically conductive plates are disposed on the board plane, the patterns must be laid out to prevent the electrically condctive plates from overlapping with each other.
FIG. 35 shows a wiring pattern example of electrical conductors also known in the conventional art. In this drawing, 901 denotes a printed circuit board, 902 designates holes, 903 and 904 indicate hook-shaped electrically conductive plates, and 905 represents a straight-line electrically conductive plate. The formation of a large-current circuit using not only the straight-line electrically conductive plate 905 but also the hook-shaped electrically conductive plates 903, 904 is generally disclosed in Japanese Laid-Open Patent Publication SH060-257191 and in Japanese Laid-Open Utility Model Publication HEI2-45665 which will be described later. Recently, there is a greater demand for more compact products without loss of freedom for parts layout. However, it is often the case that terminals cannot be arranged for electrical connection by only using straight-line conductors, and odd-shaped electrical conductors are often employed.
When electrically conductive plates are actually manufactured, straight-line electrically conductive plates may be manufactured easily by, for example, cutting a copper line. However, hook-shaped electrically conductive plates are manufactured by, for example, bending a copper line or die-cutting a copper plate with dies. Accordingly, when electrically conductive plates have complex shapes like a hook, dies must be manufactured and machined for each shape in the manufacturing of the conductors, resulting in increased equipment and jig costs and machining costs or in increased material costs for shapes that will waste materials.
FIG. 36 shows another conventional design disclosed in Japanese Laid-Open Utility Model Publication HEI-245665. In FIG. 36, 1001 indicates an insulating board, 1002A to 1002D designates electronic circuits, 1003A to 1003C represents large-current circuits, 1004 denotes drawn holes, and 1005 indicates self-clinching holes. The large-current circuits 1003A to 1003C comprising oxygen-free copper plates are formed on the same plane with the board surface of the insulating board 1001.
FIG. 37 is a sectional view of a conventional art board fastener used with a large-current circuit board disclosed in Japanese Laid-Open Patent Publication HEI2-159787. In FIG. 37, 1100 is a sectional view of a board fastener wherein 1101 indicates a cylindrical portion having an outside diameter 1103 and an inside diameter 1107 and a lip or flange portion with an outside diameter 1102.
A procedure of locking the board faster 1101 shown in FIG. 37 to a circuit board, e.g., a printed circuit board, by caulking will now be described in accordance with FIGS. 38 and 39. As shown in FIG. 38, the board fastener is inserted into a through hole 1201a provided in a printed circuit board 1201 and is pushed therein until flange 1104 makes contact with the printed circuit board 1201.
When the board fastener 1100 in the state shown in FIG. 38 is then pressed by a tool (not shown) so that it is compressed in an axial direction, a portion 1101b of the cylindrical portion 1101 protruding from the through hole 1201a of the printed circuit board 1201 is transformed, as shown in FIG. 39, to be larger in the outside diameter 1102. As shown in FIG. 39, the printed circuit board 1201 is held between the transformed portion 1301 and the flange 1104, whereby the printed circuit board 1201 and a caulked/locked body 1300 are locked with each other. The board fastener 1100 caulked to the printed circuit board 1201 is referred to as the caulked/locked body 1300.
FIG. 40 illustrates an application example of the caulked/locked body 1300. According to this application example, the board fastener 1100 is inserted into a through hole 1201s provided in the printed circuit board 1201 and caulked to be locked to the printed circuit board 1201.
Also, a screw 1401 is inserted into a through hole 1402a of a busbar 1402 and subsequently inserted into the caulked/locked body 1300 from the side of the cylindrical portion 1106, thereby protruding a threaded portion 1401a of the screw 1401 from the side of the flange 1104.
The threaded portion 1401a is screwed into a thread hole provided in a terminal 1403a of a circuit part 1403 and the screw 1401 is tightened to lock the busbar 1402 and the terminal 1403a to the caulked/locked body 1300, whereby the through hole 1201s of the printed circuit board 1201 and the caulked/locked body 1300 are connected electrically and also the busbar 1402, the terminal 1403a of the circuit part 1403, and the caulked/locked body 1300 are connected electrically, forming a large-current circuit board.
In the conventional art disclosed in Japanese Laid-Open Patent Publication HEI2-159787 and the conventional art printed board art disclosed in Japanese Laid-Open Utility Model Publication HEI2-45665, the oxygen-free copper plates or the like allow large current to flow in the plane direction of the board and the fasteners and the drawn portions of the conductors allow large current to flow also in the through hole direction. Since the electrically conductive plates are disposed on the plane in both cases, however, a pattern layout must be set to prevent the electrically conductive plates from overlapping with each other, placing large restrictions on design.
Namely, when the electrically conductive plates are complex-shaped in such cases, dies must also be manufactured and machined for each shape of conductor, resulting in increased equipment and jig costs and machining costs or in increased material costs for shapes that will leave many remainders of materials. Especially for size reduction, large-current carrying wirings must made to be higher in density but the conductor shapes become further complicated.
FIG. 41 shows another conventional design disclosed in Japanese Laid-Open Patent Publication SHO57-190335. In FIG. 41, two wirings 1502, 1503 cross each other on the surface of a mother board 1501. A small board 1504 is disposed above one wiring 1502. An air gap 1505 is provided between the small board 1504 and the wiring 1502. 1506 indicates joints and 1507 denotes solder.
On the mother board 1501, the two wirings have a crossing portion in an insulated state, the small board 1504 is placed above one wiring 1502, and the air gap 1505 is provided between the small board 1504 and the wiring 1502. In addition, the other wiring 1503 is formed on the small board 1504 to provide the crossing portion of both wirings and the metal (solder) 1507 is applied to the conductor joints of the wiring 1503, thereby reducing the electrical resistance of both wirings with the wirings kept isolated.
In this conventional design, the conductors are crossed and the wirings are made to be higher in density, thereby increasing the freedom of design. That is, since the circuit having the crossed wirings is designed to connect the electrically conductive plates in a bridge shape, the shapes of the electrical conductors can be relatively simplified. Unfortunately, the bridge-shaped electrically conductive plates require the number of machining processes and the number of parts to increase and have disadvantages in costs and work required.
As an application example of such conventional crossed wiring art, wherein a bridge-shaped busbar as shown in FIGS. 42a and 42b is placed on a circuit board, have actually been put to practical use. In FIGS. 42a and 42b, 1601 indicates a printed circuit board and 1602 denotes a bridge-shaped busbar. 1603, 1604 and 1605 indicate straight-line busbars.
The bridge-shaped busbar 1602 allows a large-current circuit to be multi-layered in part. However, a plate-shaped material must be machined to have a bridge shape. In order to manufacture the bridge-shaped busbar 1602, predetermined dimensions are required for retaining parts during the machining or for boring or bending, e.g., predetermined radii are required for bending. In addition, wiring and assembling the bridge-shaped busbar requires high accuracy for position setting due to its complex shape.
Having the aforementioned dimensional restrictions, the bridge-shaped busbar is sized to greater than the dimensions required for wiring. In other words, as shown in FIGS. 42a and 42b, the minimum value of a distance 1606 between the busbars 1604 and 1605 is determined by a dimension required to manufacture the bridge-shaped busbar and by an insulation distance. To make the bridge-shaped busbar 1602 smaller, the dimensions required to manufacture the bridge-shaped busbar must be reduced.
Any of the conventional art large-current circuit boards arranged as described above allows large current to flow in the plane direction of the board and its fasteners and drawn portions of the conductors allow large current to flow also in the through hole direction. However, since the electrically conductive plates are disposed on the board plane, the pattern layout must be set to prevent the electrically conductive plates from overlapping with each other, placing large restrictions on design.
Especially for size reduction, the large-current carrying wirings must be made to be higher in density, but the conductor shapes must be complicated, such as a hook, and dies must be manufactured and machined for each shape in the manufacturing of the conductors, resulting in increased equipment and jig costs and machining costs or in increased material costs for shapes that will leave many material remainders.
Also known in the art is another large-current circuit board which has crossed conductors, high-density wirings and increased freedom of design. Since the circuit board including the crossed wirings is designed to connect the electrically conductive plates in a bridge shape, the shapes of the electrical conductors can be relatively simplified, but the bridge-shaped electrically conductive plates require a number of machining processes and a number of parts to increase and have disadvantages in costs and work.
Also, since the fasteners are caulked and secured to the board, the reliability of the circuit board was not sufficiently high.
It is accordingly an object of the present invention to overcome the disadvantages in the conventional art by providing a large-current circuit board which allows comparatively large current to flow in both a plane direction and a through hole direction of a circuit board, allows wirings to be high in density, ensures ease of manufacturing busbars and fitting the same to the circuit board, and facilitates assembling and automation.
Another object of the present invention is to provide a large-current circuit board which is high in reliability.